Coatings or decorative sheets are mainly used as decorating materials for furniture, sinks, doors, and the like.
For coating materials an UV-curing high gloss paint has been used, but it can realize only a single color and has the problem of yellowing after painting and lowering of gloss as time passed.
Conventionally, polyvinyl chloride (PVC) sheets have been used as decorative sheets. With various advantages such as low price, excellent processability, thermal deformability, excellent elongation, and the like, PVC sheets have been widely used for a variety of products.
However, PVC sheets have a problem of generating a large amount of dioxin upon burning. Dioxin is a typical endocrine disruptor that is extremely stable and resistant to decomposition. Thus, once absorbed into the human body, dioxin is not easily discharged from the body and accumulates therein. As a result, dioxin can cause cancer, severe reproductive system disorders, developmental disorders, and the like. Moreover, dioxin can damage the endocrine system.
Due to harmfulness of polyvinyl chloride on the human body, regulations concerning polyvinyl chloride-based products are being strengthened.
In recent years, to replace polyvinyl chloride, environmentally friendly materials have been developed, and polyesters-based sheets, i.e., polyethylene terephthalate (PET) sheets are proposed.
PET sheets have a high quality surface, while they require a higher molding temperature and a narrower molding temperature range than a PVC sheet. Therefore, PET sheets have the problem that they do not have good moldability. Moreover, PET sheets have limitations in coating for improving hardness and cause a high rate of defects due to crystallization.
Further, when PET sheets employ a large amount of additives for the purpose of improving moldability, it is difficult for securing a uniform printability.
To remedy such disadvantages the PET sheets, PETG sheets are proposed. PETG, an amorphous polymer, does not cause defects due to crystallization and is easily coated on surfaces, thereby being useful for decorative sheets. However, PETG has the disadvantage that its cost is higher than PET by about 30%.
Moreover, decorative sheets for indoor use require a surface hardness since they are exposed to frequent scratches.
In order to give a scratch resistance, decorative sheets are coated with hard coating layer on the top surface layer.